Elected in 2010 after a bruising race against former Rep. Stephanie Herseth-Sandlin (D-SD), Noem has earned star status among fellow Republicans and the tea party faithful. Varilek, a former staffer for Sen. Tim Johnson (D-SD), won the Democratic Party's nomination in June.

Nielson Brothers conducted its survey July 19-23 with 541 registered voters in South Dakota. The poll has a margin of error of 4.21 percentage points.